import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class SubstringWithConcatenationOfAllWords {
    // 串联所有单词的子串 https://leetcode.cn/problems/substring-with-concatenation-of-all-words/description/
    public List<Integer> findSubstring(String s, String[] words) {
        List<Integer> ret=new ArrayList<>();
        Map<String,Integer> hash1=new HashMap<String,Integer>();//保存words中字符串的频次
        for(String str:words) {
            hash1.put(str,hash1.getOrDefault(str,0)+1);
        }
        int len=words[0].length(),m=words.length;
        for(int i=0;i<len;i++) {    //滑动窗口的完整遍历次数
            Map<String,Integer> hash2=new HashMap<String,Integer>();// 保存窗口内字符串的频次
            for(int left=i,right=i,count=0;right+len<=s.length();right+=len) {
                // 进窗口+维护count
                String in=s.substring(right,right+len);
                hash2.put(in,hash2.getOrDefault(in,0)+1);
                if(hash2.get(in)<=hash1.getOrDefault(in,0)) count++;
                // 判断
                if(right-left+1 > len*m) {
                    // 出窗口+维护count
                    String out=s.substring(left,left+len);
                    if(hash2.get(out)<=hash1.getOrDefault(out,0)) count--;
                    hash2.put(out,hash2.get(out)-1);
                    left+=len;
                }
                // 更新结果
                if(count==m) ret.add(left);
            }
        }
        return ret;
    }

}
